Fuzhou Xiaoyu recruitment

When observing the tail fin of a small fish with a microscope, the basis for judging arteries, veins and capillaries is: the blood vessels flowing from the main trunk to the branches are arteries, in which the blood flows faster; The blood vessels formed by the confluence of branches are veins, in which the blood flow is relatively slow; Capillary is the blood vessel connecting the smallest artery and the smallest vein. Capillary is characterized by the thinnest lumen, allowing only red blood cells to pass through in a single file, the thinnest wall, only a layer of epithelial cells, and the slowest blood flow rate, which are beneficial to the exchange of substances between blood and tissue cells. As can be seen from the blood flow direction in the figure, the nail vessel is a vein from the branch to the trunk; The second blood vessel flows from the trunk to the branch, so it is an artery; Blood vessel C is connected with the smallest artery and the smallest vein, so it is a capillary.

So choose: B.